Today's electronically controlled compression ignition engines typically include an electronically controlled fuel injector with a direct operated check valve. The direct operated check valve includes a closing hydraulic surface exposed to pressure in a needle control chamber. Pressure is relieved in the needle control chamber to initiate an injection event by actuating a two way or three way valve to fluidly connect the needle control chamber to a low pressure drain outlet. The injection event is ended by de-energizing the electronically controlled two way or three way valve to repressurize the needle control chamber. Co-owned U.S. Pat. No. 7,331,329 shows an example of such a fuel injector with a three way valve, whereas U.S. Pat. No. 6,986,474 shows an example fuel injector with a two way valve. In general, a three way valve version can provide greater performance capabilities relative to a two way valve counterpart, but does so at the expense of increased complexity and difficultly to manufacture, especially mass producing fuel injectors with consistent performance behaviors.
Early versions of the two way valve typically included the needle control chamber fluidly connected to a nozzle supply passage via an unobstructed Z orifice, and the two way valve permitted fluid communication between the needle control chamber and a low pressure drain outlet through a so called A orifice. During an injection event, the nozzle supply passage is fluidly connected directly to the low pressure drain via the Z orifice, the needle control chamber and the A orifice. Thus there was an initial motivation to make the A and Z orifices relatively small in order to reduce losses during an injection event. This motivation quickly lead to a problem associated with a general desirability to end injection events abruptly, which is accomplished by quickly raising pressure in the needle control chamber. A small Z orifice slows the rate at which pressure may grow in the needle control chamber at the end of an injection event. This problem was addressed by adding an additional orifice to facilitate the quick repressurization in the needle control chamber toward the end of injection event. For instance, previously identified U.S. Pat. No. 6,986,474 includes an additional orifice 14 that facilitates repressurization of its needle control chamber 4 via both the Z orifice 5 as well as through the A orifice 6 by way of the additional fill or F orifice 14. The three way valve fuel injector counterpart identified above in co-owned U.S. Pat. No. 7,331,329 likewise includes three orifices, which include a Z orifice 112, and two other orifices 110 and 111, that most closely resemble in performance the F orifice and A orifice, respectively for the counterpart two way valve fuel injector.
Because of the complexity and difficulty in manufacturing a three way valve that performs consistently with mass produced fuel injectors, there is a growing desire toward utilizing a two way control valve to perform the pressure control function in a direct control check valve for a fuel injector. Unfortunately, current strategies with regard to utilization of two way valves, even with the inclusion of F, A and Z orifices, result in less than satisfactory performance relative to the counterpart three way valve control strategy. For instance, while the inclusion of an F orifice can aid in hastening the end of an injection event, the F orifice may not assist in retarding the rate at which the needle valve member opens to commence an injection event, which is also sometimes a desirable fuel injector attribute. In addition, variations in flow areas among control valves for mass produced fuel injectors can result in an unacceptable variance in performance among the fuel injectors.
The present disclosure is directed to one or more of the problems set forth above.